The goal of this project is to study the mechanisms which regulate the expression of viral sequences in cells infected by Moloney murine sarcoma virus (MSV). The structure and expression of mouse and human cellular sequences which are homologous to the transforming gene of MSV will also be investigated. The intergrated proviral DNA contains long terminal direct repeats (LTR) which are generated during reverse transcription. The LTRr contain information which iscrucial to several parts of the virus life cycle including integration, transcription and replication. Preliminary data support the notion that MSV is transcribed as an independent unit. I propose to study in detail processes involved in initiation and termination of transcription and mRNA formation. Nascent nuclear virus-specific RNA chains and mature stable viral RNAs will be identified and mapped by hybridization to viral DNA clones which represent different portions of the viral genome. Virus-specific messenger RNA formation will also be studied by characterizing recombinant cDNA clones obtained by reverse transcription of mRNA from MSV infected cells. The relationship between viral gene expression and neoplastic transformation will be analyzed in a series of cellular clones which contain a fully competent viral genome but have reverted to a normal phenotype. A detailed study of the mechanisms by which viral gene expression is repressed in these clones should provide information on how cellular genes are regulated. In particular it is hoped that the proposed research will contribute to a better understanding of the relationship between the formation of viral oncogenes and the role of their cellular precursor sequences in normal uninfected tissues.